It is our hypothesis that healing of ligaments and tendons is a long-term process that involves a return in strength due to callus formation, followed by long-term remodelling of the collagen involving changes in fiber alignment, ground substance, and cross-linking. We further hypothesize that the extent to which a blood supply is available has a significant effect on the return in strength. Repairs in relatively vascular regions and free grafts need protection for prolonged periods of time. On the other hand, the presence of a profuse vascular supply may permit a more rapid return in strength, allowing earlier motion, earlier rehabilitation and return to normal activity with less disuse effects. To test these hypotheses we will measure the return in strength and biochemical remodelling over time of selected primary repairs and grafts in activity conditioned, skeletally mature beagles. The following specific situations will be studied. Primary Repairs: 1) We will compare flexor tendon repairs in highly vascular paratenon regions to repairs in the synovial sheath, a comparatively avascular region; 2) An anterior cruciate mid-substance partial injury will be studied with and without the use of fat pad sutured to the ligament to provide an additional source of blood supply; 3) Healing in the medial collateral ligament will be determined for complete mid-substance tears induced at the time of surgery. Grafts: 1) A bone-patellar tendon-bone free graft substitute for the anterior cruciate ligament will be compared to the same graft that incorporates a tissue flap that provides its blood supply. 2) A flexor tendon autograft will be compared with an allograft. In the first year we will document the local blood supply using microangiography and refine the surgical techniques, particularly to avoid interruption of the blood supply. We will also verify our existing gripping methods for mechanical testing of the isolated tendons. During the second and third years of the project we will measure both the return in strength and the biochemical changes in each model.